The present invention relates to a lockup control device for a transmission with a lockup torque converter.
Normally, in a vehicle provided with a transmission fitted with a torque converter, the torque converter is provided with a lockup clutch. When the lockup clutch is edged and the torque converter is locked, the torque converter no longer slips, the engine rotation speed can be decreased by a corresponding amount, and fuel cost performance is increased.
The lockup clutch normally engages when the vehicle running condition is in a predetermined lockup region. However, the operation of the lockup clutch is not stable when the transmission oil temperature is still low, so lockup must be prevented. In the prior art, the transmission oil temperature is compared with a predetermined threshold value. When the oil temperature is lower than the threshold value lockup is prohibited, whereas when it is higher than the threshold value lockup is permitted.
When the engine is warming up, lockup, which is a factor responsible for decreasing the engine rotation speed, must be prevented to increase the catalyst temperature and to enhance the activity of the catalyst. In the prior art, it is determined whether or not to permit or prohibit lockup by comparing the engine cooling water temperature with a threshold value. Alternatively, it is determined whether to permit or prohibit lockup by determining whether the elapsed time since startup has reached a predetermined time which is set according to the transmission oil temperature on startup, as disclosed in JP-B2-2903456 published by the Japanese Patent Office in 1999.
However, if it is determined whether to permit or prohibit lockup by comparing the transmission oil temperature or engine cooling water temperature with a predetermined value, as these temperatures fluctuate due to the effect of oil flow or change-over of cooling water flow due to a thermostat, lockup may be repeatedly prohibited and permitted due to these fluctuations about the threshold values, and hunting may occur in the lockup control.
Hunting may be suppressed to some extent by incorporating hysteresis in the threshold value used for the determination, but if a fluctuation of transmission oil temperature or engine cooling water temperature in excess of the hysteresis, the same effect will take place.
Further, in the method disclosed in JP-B2-2903456, lockup is not prohibited again once it has been permitted, so hunting does not occur. However, the determination is not based on the real transmission oil temperature or engine cooling water temperature, so the transmission oil temperature or engine cooling water temperature when lockup is permitted, varies with the running state on startup. In other words, the running state wherein lockup is permitted fluctuates.
It is therefore an object of this invention to prevent hunting in lockup control and permit lockup in the same running state, when lockup is prohibited when the transmission oil temperature is low or engine cooling water temperature is low.
In order to achieve above object, this invention provides a lockup control device for a transmission having a torque converter with a lockup clutch, comprising a first sensor which detects a parameter which varies according to a warmup state of a vehicle, a second sensor which detects a running state of the vehicle, and a microprocessor programmed to determine whether warmup is complete based on the parameter, enable to engage the lockup clutch once the microprocessor has determined that warmup is complete, and control the engagement of the lockup clutch according to whether or not the running state is in a predetermined lockup region when it is determined that warmup is complete.
According to an aspect of the invention, this invention provides a lockup control device for a transmission having a torque converter with a lockup clutch, comprising a first sensor which detects a parameter which varies according to a warmup state of a vehicle, a second sensor which detects a running state of the vehicle, and a microprocessor programmed to determine whether warmup is complete based on the parameter only when the lockup clutch is disengaged, and control the engagement of the lockup clutch according to whether or not the running state is in a predetermined lockup region when it is determined that warmup is complete.
According to another aspect of the invention, this invention provides a lockup control device for a transmission having a torque converter with a lockup clutch, comprising a first sensor which detects a parameter which varies according to a warmup state of a vehicle, a second sensor which detects a running state of the vehicle, and a microprocessor programmed to determine whether warmup is complete based on the parameter, determine a lockup permission condition is present when it is determined that warmup is complete or when it is determined that warmup is not complete and the lockup clutch is engaged, and control the engagement of the lockup clutch according to whether or not the running state is in a predetermined lockup region when it is determined that the lockup permission condition is present
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.